A movable reflective device capable of tilting a reflective surface is used as a device for controlling the direction of light beams or directional radio waves. Particularly, the movable reflective device capable of tilting the reflective surface with two axes of freedom is used as an installed component for various electronic devices since such a movable reflective device can be used as a two-dimensional scanner for two-dimensional scanning of light beams or the like. For example, the movable reflective device additionally provided with a driver for supplying electrical signals can implement a reflective surface drive system with functions of controlling a reflective surface at an attitude, and thereby can be applied to a projector for projecting images, an onboard radar, or the like. The movable reflective device has been recently installed in a mobile device such as a smartphone, and micro electro mechanical system (MEMS) technology is used to put a compact and low-voltage driven device into practical use.
A typical movable reflective device currently in use has a configuration in which a mirror with a reflective surface is supported by plate-like arms and piezoelectric elements are attached to the plate-like arms. Application of a predetermined electrical signal to the piezoelectric elements causes desired deformation of the arms, which results in tilting of the mirror in a desired direction. Use of a direct-current signal as the electrical signal keeps the reflective surface at a desired attitude, while use of an alternating-current signal as the electrical signal vibrates the reflective surface in a desired direction.
For example, Patent Literature 1 below discloses a movable reflective device in which a mirror is driven by causing flexure of piezoelectric members. Patent Literature 2 discloses use of a so-called gimbal structure in which inner gimbal frame is attached to outer gimbal frame to be freely rotatable about a first rotation axis, and a mirror is attached within the inner gimbal frame to be freely rotatable about a second rotation axis perpendicular to the first rotation axis. Patent Literature 3 discloses a movable reflective device provided with a sensor for detection of stress on a connection so that a tilt angle of a mirror is detectable.
Patent Literature 4 discloses a reflective surface drive system that drives piezoelectric actuators with a sawtooth-waveform electrical signal. Patent Literature 5 discloses a MEMS-device reflective surface drive system having a projector function.